In industrial machining operations lubricating oils, sometimes called "tramp" oils, come in contact with the parts being machined. Much of this tramp oil remains on the surface of the machined parts or chips and is carried to subsequent operations. In these subsequent operations, the tramp oil can enter the recycled cooling fluid. If tramp oil is allowed to accumulate in a coolant or washer system it can cause operating problems, such as machine down-time, increased tool wear, cleaning and filtering problems, and possibly allowing bacteria to grow in the oil accumulated in the system. As a result of these problems, the coolant's effectiveness and useful life are reduced. Preventive maintenance and good housekeeping practices help reduce, but never completely eliminate, tramp oils.
One solution to this problem is to throw out the used coolant solution, replacing it with fresh. This solution, however, is expensive and impractical. Oil-contaminated coolant has recently been classified as hazardous waste, making disposal extremely costly. In addition, the coolant itself is expensive. Therefore, various methods to remove oils front coolant systems have been developed, some of which are discussed below.
Large gravity separators and extractors that rely on either centralized or portable pumping systems have been used in an attempt to separate oil from coolant solutions. These systems are expensive to purchase, require a significant amount of power to operate, are large and bulky, and require time and training to use. Such a system is disclosed in U.S. Pat. No. 5,053,145 to Ellison.
Additionally, a variety of small oil removal devices which operate unattended have been developed. These include drum, belt and disk oil skimming or collection devices. Each of these, however, has shortcomings. Drum devices are the least desirable; they take up the largest amount of space of the three types listed above and remove a large quantity of coolant along with the oils.
Belt devices can access any depth of coolant, but also remove large amounts of coolant along with the oil. In addition, the belt material may be affected by the chemical composition of the coolant or the heat of the wash water. This is discussed in U.S. Pat. No. 4,614,582 to Campitelli.
Disk skimmers also tend to remove much of the coolant along with the oil. They cannot reach as great a depth as the belts, primarily due to the fact that the disk diameter is relatively small and the disk is mounted relatively high above the water. The surface of the disk, therefore, extends only a few inches into the coolant/oil mixture to be separated. In addition, during operation solids impact the disk, chipping or deeply scoring the disk. The disk then removes even more of the coolant, further degrading its performance.
A disk skimmer described in U.S. Pat. No. 5,167,815 issued to Bachmann et al. has addressed one problem described above by the use of a flotation device and a parallel arm arrangement to enable the disk to skim from varying fluid levels. It uses a screw mechanism and floating arrangement to separate the oil from the coolant. This design, however, is bulky and expensive. Further, the problem of the disk removing excessive amounts of coolant, however, is not resolved by this device.
In summary, the known small, unattended oil-removal devices, such as disk skimmers, have the following limitations:
A) They tend to remove excessive amounts of coolant or wash water along with the oils,
B) Their performance degrades as the disk or pickup media wears,
C) They require a large area for mounting onto the machine on which they will be used; this area is more than many machines can permit,
D) Disk skimmers cannot handle wide fluctuations in fluid levels because the disk does not extend deeply into the coolant/oil solution,
E) Current disk skimmers are heavy and bulky,
F) Current designs require many manufacturing steps and require assembly by the user,
G) Current designs cannot be easily adapted to incorporate a separate module for separation of the oil and the water,
H) Current disk skimmer designs force the user to separate oil from the water in a second, secondary process step, and
I) Current gravity separators used with oil removal devices are large, expensive and impractical.